1. Field of the Invention
The present invention relates to method and apparatus for severing a tubular wherein the method and apparatus are operative to be used to severe tubulars of differing dimensions and/or a tubular having a constriction(s) along the length thereof, and more particularly, to such method and apparatus in which liquid explosive, which is contained within the apparatus and which is initially constrained against movement, is placed in close proximity to the tubular and detonated to sever the tubular.
2. DESCRIPTION OF RELATED ART
During drilling of a subterranean well, a drill string comprised of lengths of drill pipe connected by couplings may become stuck within the well bore being drilled. Due to the expense of such pipe, it is desirable to cut or severe the stuck drill string so that the maximum amount of drill pipe can be removed to the surface of the earth and salvaged for future operations. In workover operations in which tools are positioned downhole by means of tubing, the tubing and/or tool(s) may become stuck for a variety of reasons, such as mechanical failure of the tool(s) or build up of debris, and severing the tubular for removal from the well and salvage may be desirable. It may also be desirable when abandoning a well to severe the well casing above the position where such casing is cemented in a well for salvage.
Explosive jet pipe cutters which are lowered into a subterranean well by means of an electrical wireline are conventionally utilized to severe stuck pipe within the well. Such cutters are dimensioned to have an external diameter slightly less than the smallest diameter of the tubular to be severed. Thus, different diameter cutters are needed depending upon the exact diameter of the tubular to be severed. An electric detonator in the device is actuated by means of electrical current which is transmitted from a supply at the surface by means of the wireline. The detonator in turn detonates a high explosive, radially shaped charge which severs the pipe adjacent the explosion.
Conventional explosive severing tools are constructed of a relatively large quantity of explosive suspended within a tubular which is stuck in a well bore by means of a detonating cord. Upon detonation, the force of the explosion is radiated in all directions. As with conventional jet cutters, conventional explosive servering tools are sized to minimize the circumferential gap between the periphery of the tool and the tubular to be severed.
A significant drawback to the use of conventional explosive jet cutters or severing tools to severe stuck tubing or pipe within a well is that such cutters or tools are often sized sufficiently large, for example 23/8 inch outer diameter, to be unable to pass through restrictions created by tubing or pipe which is damaged, i.e. bent or partially collapsed, but not stuck within a well. For this reason, conventional cutters are often unable to severe and remove a significant portion of tubing or pipe from a tubing string which is stuck in a well. Thus, a need exists for a method and apparatus capable of passing through restrictions within a tubing or pipe which is stuck within a well.
Accordingly, it is an object of the present invention to provide method and apparatus for severing a tubular which is stuck within a well wherein the apparatus is capable of passing through restrictions within the tubular so as to be positioned at a desired depth.
It is another object of the present invention to provide method and apparatus for severing a tubular which is stuck within a well wherein the apparatus is capable of being expanded so as to move liquid explosive into close proximity to the tubular upon being positioned at a desired depth.
It is a further object of the present invention to provide method and apparatus for severing a tubular wherein the transportation of explosives from a surface location to a subterranean location during operation of the apparatus and the attendant hazards associated therewith are obviated.
It is a still further object of the present invention to provide method and apparatus for severing a tubular wherein the apparatus is constructed and the method is carried out in a manner so as to enable one apparatus to be utilized in tubulars of all diameters which might be encountered within a well.